[CMake] How to get Visual Studio to use more than a single core for compiling

[John Drescher]

> Right, perhaps complex inter-project dependencies halt the processes.

I believe this is part of the reason. Projects like ITK with hundreds
of small utilities tend to utilize the cores after the dependent
libraries are built however my code that has very few utilities and
significantly more inter-project dependencies do not tend to make good
use of the cores.

On top of that it appears that VS building slows down significantly as
the # of include folders greatly increases. This cuts into CPU
utilization when the OS searches your includes for your header files.
In the past I have tried to get around the inter-project dependency
problem by building Release, Debug and RelWithDebInfo in 3 separate
processes only to find that on some builds this did not fix the issue
because the OS spent an a large portion of the build time searching
the include paths. I even tried to stop this by placing the projects
and includes on a RAM disk but even that did not totally fix the
issue.

John